As reported earlier, the second half of this century would witness sever, mega-drought in the U.S. Southwest and Central Plains, which could be drier and longer than ever seen in the last 1,000 years, going by a new NASA study.

Ben Cook, climate scientist at NASA’s Goddard Institute for Space Studies and the Lamont-Doherty Earth Observatory at Columbia University in New York City, and lead author of the study says: “We’re going to get a drought… probably going to last at least 30 to 35 years.”

Cook attributes the likelihood of the megadrought at 12 percent now but if greenhouse gas emissions fail to stop even after 20150, then there is 80 percent likelihood and in another scenario, in case greehouse emissions are arrested by 2050, then the likelihood me be down to 60 percent but not less than that.

Analyzing a drought severity index and two soil moisture data sets from 17 climate models that were run for both emission scenarios, the scientists said the high emissions scenario projects the equivalent of an atmospheric carbon dioxide concentration of 1,370 parts per million (ppm) by 2100, while the moderate emissions scenario projects the equivalent of 650 ppm by 2100 compared to current 400 ppm of CO2.

Supporting the findings, Kevin Anchukaitis, a climate scientist at the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts, who was not involved in the study, says: “What I think really stands out in the paper is the consistency between different metrics of soil moisture and the findings across all the different climate models.”

There are reasons why this study is an early warning to the current generation. It is the first to compare future drought projections directly to drought records from the last 1,000 years. Its measurements of drought indicators go back about 150 years. Further, Cook and his colleagues used a well-established tree-ring database to study older droughts.

Centuries-old trees allow a look back into the distant past, especially in tree species like oak and bristle cone pines, which grow more in wet years, leaving wider rings, and vice versa for drought years. Measuring drought through these tree rings can help the scientists to establish moisture conditions in the past 1,000 years.

Moreover, the scientists studied megadroughts that took place between 1100 and 1300 in North America, known as medieval-period droughts, on a year-to-year basis, and were no worse than droughts seen in the recent past. In some cases, they lasted well over 30 to 50 years.

When these past megadroughts are compared side-by-side with computer model projections of the 21st century, both the moderate and business-as-usual emissions scenarios are drier, and the risk of droughts lasting 30 years or longer increases significantly.

Connecting the past, present and future in this way shows that 21st century droughts in the region are likely to be even worse than those seen in medieval times, says Anchukaitis.